Clean up workers dressed in protective work at the former K-25 site in Oak Ridge. (J. MILES CARY/NEWS SENTINEL)

OAK RIDGE — The government has invested extraordinary resources over the past 30 years to deal with environmental legacies of the nuclear weapons program, which began with the World War II Manhattan Project. Mountains of radioactive waste have been moved, and a lot of cleanup has been accomplished. But a lot remains to be done — and it won’t be cheap.

The U.S. Department of Energy estimates it will need $12 billion to finish the Oak Ridge cleanup work by 2046, the completion date DOE negotiated with environmental regulators.

The completion date and the overall cost could be affected by how much funding Congress appropriates for the cleanup program and how wisely and efficiently the money is spent.